Simplifying Schematics

December 15, 2009 | Reply More


As every technician knows, one of the most challenging tasks in the automotive field is electrical diagnosis. This is compounded by ever more complex vehicles. Whether it is for efficiency in manufacturing, or for more integrated features, electronic control units are being asked to handle almost every aspect of motorized transportation. While this does lead to a reduction in wiring, it also makes factory self-diagnostic software essential to diagnosing problems in these integrated computer networks.

Regardless of all the new complexity, you still need to come up with a diagnostic plan that will find problems efficiently and effectively, thus allowing your shop to remain profitable. With electrical problems, inadequate supply voltage, component current draw and excessive voltage drop add up to troubleshooting complications.  An essential here is understanding how the circuit works, but this is one aspect we are in control of.  Knowing how to read and interpret BMW wiring diagrams accurately is half the battle (the other half is actually testing voltages, resistances and amperages). Here, we are going to review navigating the BMW website for the proper wiring diagrams, and some of the benefits of BMW factory wiring.


BMW TechInfo

our paid subscription to gets you access to factory service information. Under “Wiring Diagrams,” select “Wiring Diagram Systems from E38” and you will be directed to installing WDS wiring.


At the beginning of any diagnosis, you need a firm grasp of the symptoms and what systems on the vehicle could possibly cause them. Before you start ripping off panels and covers to access wiring, you should pull up the wiring diagrams for the circuits you believe might be at fault. With your paid subscription, you will have access to accurate factory diagrams. This is especially valuable when it comes to the variants of the model — not only the various options, but also any changes that may have occurred from one production run to another. This vehicle-specific information is not always available from the aftermarket information sources you may currently be using.

On the homepage under the heading “Wiring Diagrams,” you will see two options. The first is for selecting the E36 chassis or earlier vehicles. These are PDFs (Portable Document Files), so you will need to have Adobe Acrobat Reader on your computer to view them. They are scanned images of factory paper manuals. You navigate through the various pages by scrolling with the bar on your right and at the bottom just as you do with any file folder in Windows or MAC Explorer. All the information is there, you just have to move the screen around to see it because these pages were not intended to be PC-based. Your other selection is for BMWs built after the E36 chassis, which are probably most of the vehicles you work on. These diagrams were constructed with PC navigation in mind, so all of the variations are laid out like the folders in Windows Explorer, but more on that later.

After selecting post-E38 diagrams, you


Login to continue reading this article.

Not a member? Register for FREE access.

Lost your password?

Category: BMW TechDrive

Leave a Reply

You must be logged in to post a comment.